1. Field of the Invention
The present invention relates generally to a transmitting and receiving apparatus and method for optimizing performance of an adaptive modulation and coding (AMC) in a multiple input and multiple output antenna (MIMO) communication system. More specifically, the present invention relates a transmitting apparatus of a MIMO system, which includes an ordering selector that selects a successive interference cancellation (SIC) scheme to obtain a maximum MIMO-AMC performance, and a receiving apparatus, which includes a channel quality information (CQI) generator (a MIMO equivalent channel generator) corresponding to the SIC scheme selected at the transmitting apparatus.
2. Description of the Related Art
Multiple input and multiple output antenna (MIMO) technologies have been introduced for increasing a transmission data rate. An example of MIMO technology is spatial multiplexing (SM), which enables high-speed data transmission by transmitting different data via multiple transmit (Tx) antennas. Recently, in MIMO systems, space-time coding (STC) has been proposed, which can obtain a diversity gain by transmitting the same data via multiple Tx antennas. However, high SM gain and maximum diversity gain cannot be obtained at the same time. Accordingly, the STC for maximizing the diversity gain has difficulty in maximizing the transmission data rate. Although many attempts have been made to simultaneously obtain the SM gain and the diversity gain, these technologies have not been yet implemented in real applications.
There is proposed a technology for increasing the transmission data rate in the MIMO system, that is, for obtaining the maximum SM gain. More specifically, there is proposed a technology for increasing transmission rate when an adaptive modulation and coding (AMC) is applied to the MIMO system. Hereinafter, the performance of the AMC in the MIMO system means a transmission data rate when AMC is applied to a MIMO system. In addition, the terms: transmitting apparatus, transmitter, or transmitting terminal will be used interchangeably.
As one of methods for increasing the transmission data rate in the MIMO system, MIMO channel information measured at a receiver is fed back to a transmitter and an AMC is applied, thereby maximizing system capacity. Practically, it has been known that a channel capacity in the MIMO channel can be maximized using a singular value decomposition (SVD). However, when the SVD is performed an accurate channel value must be known. In a real system, a receiver estimates a channel value and transmits it to a transmitter through a feedback channel. Serious errors may occur during this process.
For the MIMO channel, a plurality of receive (Rx) antenna channel estimation values, which are transmitted from a plurality of antennas, are fed back. Therefore, a large number of the feedback values cause the serious degradation of performance due to error. Accordingly, the application of the SVD to the real system is not practical.
Another technology is a Vertical Bell Laboratories Space Time (V-BLAST). According to V-BLAST technology, a transmitter transmits independent signals through a plurality of Tx antennas, and a receiver differentiates the transmitted data through an appropriate signal processing. The receiver can obtain satisfactory performance using a successive interference cancellation (SIC) method. The SIC method includes a forward ordering policy and a reverse ordering policy. Of the two, the forward ordering policy is typical.
According to the forward ordering policy, MIMO equivalent channels distorting signals transmitted through Tx antennas are removed from MIMO equivalent channel with the highest gain. Accordingly, the forward ordering policy can prevent serious performance degradation occurring in error transmission. However, this prevention of the performance degradation is achieved when the AMC is not applied to the transmitter.
When the AMC is applied to the MIMO system, a feedback channel value based on the forwarding ordering policy is varied depending on channel states because the AMC is determined not by a general MIMO channel but by a MIMO equivalent channel, and its value is varied depending on the ordering policies. Accordingly, when the AMC is applied, it has to be determined which of the forward ordering policy and the reverse ordering policy is good. In addition, parameters necessary for determining the ordering policy need to be selected and the reference needs to be determined.